The present invention relates to a novel halogenated aromatic compound, a polyarylene (co)polymer obtained by the polymerization of such a halogenated aromatic compound as a monomer component, and a proton-conductive membrane comprising a sulfonation product of such a (co)polymer. It is known that a proton-conductive membrane can be used as a proton-conductive membrane for primary battery electrolyte, secondary batter electrolyte, fuel cell polymer solid electrolyte, display element, various sensors, signal medium, solid capacitor, ion exchange membrane, etc.
Electrolytes are usually used as (aqueous) solutions in many cases. In recent years, however, there is a growing tendency to replace such aqueous electrolytes with solid electrolytes. The first reason for this is the easiness of processing in applications of solid electrolytes, e.g., the electrical/electronic materials mentioned above. The second reason is the trend toward reduction in weight, thickness, length and size, and toward energy saving.
Conventional proton-conductive materials include both inorganic materials and organic materials. Examples of the inorganic materials include uranyl phosphates which form hydrates. However, these inorganic compounds are insufficient in interfacial contact to pose many problems concerning the formation of a conductive layer on a substrate or electrode.
On the other hand, examples of the organic compounds include organic polymers such as polymers belonging to the so-called cation-exchange resins, e.g., sulfonated vinyl polymers such as sulfonated polymers with a perfluoroalkylsulfonic acid represented by Nafion (manufactured by E. I. Du Pont de Nemours and Co., Inc.), and perfluoroalkylcarboxylic acid polymers, and polymers prepared by incorporating sulfonic acid groups or phosphoric acid groups into heat-resistant polymers such as polybenzimidazole and poly(ether ether ketone)s [see Polymer Preprints, Japan, Vol. 42, No. 7, pp. 2490-2492 (1993); Polymer Preprints, Japan, Vol. 43, No. 3, pp. 735-736 (1994); and Polymer Preprints, Japan, Vol. 42, No. 3, p. 730 (1993)].
These organic polymers are usually used in the form of a film. A conductive membrane made of such an organic polymer can be bonded to an electrode while taking advantage of the solvent solubility or thermoplasticity. However, many of these organic polymers have the following problems besides being still insufficient in proton conductivity. The organic polymers deteriorate in durability or in proton conductivity at elevated temperatures (100xc2x0 C. or higher). When sulfonated, the organic polymers undergo embrittlement, deteriorate in mechanical strength and have a great dependence on humidity conditions. Further, the adhesion of the organic polymers to the electrode is not fully satisfactory. Moreover, the conductive membrane swells excessively during operation due to the hydrophilic polymer structure, and this swelling leads to a decrease in strength properties or a deformation. Consequently, application of those organic polymers to the aforementioned electrical/electronic materials and the like pose various problems.
U.S. Pat. No. 5,403,675 proposes a solid polymer electrolyte comprising a sulfonated rigid polyarylene. This polymer is produced from a polymer comprising a phenylene chain obtained by polymerizing an aromatic compound (the polymer structure is described at column 9 in the patent specification) by reacting the phenylene polymer as the main component with a sulfonating agent to incorporate sulfonic acid groups thereinto. However, the incorporation of a large amount of sulfonic acid groups results in a sulfonated polymer having considerable deterioration in mechanical properties such as toughness (e.g., elongation at break, flexing resistance) and hot water resistance although proton conductivity improves with the increasing amount of sulfonic acid groups incorporated.
Accordingly, one object of the invention is to provide a (co)polymer that is superior in mechanical properties such as oxidation resistance, hot water resistance, heat resistance, and toughness and that even when sulfonated, the association efficiency is high so that even when the incorporation amount of sulfonic acid groups is relatively low, not only it has efficient proton conductivity, but also it hardly deteriorates in the aforementioned properties.
Another object of the invention is to provide a sulfonic acid group-containing (co)polymer obtained by sulfonating the (co)polymer.
Still another object of the invention is to provide a proton-conductive membrane comprising the sulfonic acid group-containing (co)polymer that is superior in the aforementioned properties and has efficient proton conductivity.
These objects of the invention will become apparent from the following detailed description and examples.
First, the invention is to provide a compound useful as a monomer effective for the incorporation of sulfonic acid groups in a (co)polymer. The compound is a halogenated aromatic compound represented by the following general formula (1bm): 
wherein Asxe2x80x2 independently represent an electron-withdrawing group; Bsxe2x80x2 independently represent an electron-donating atom or divalent group; Xsxe2x80x2 independently represent a chlorine atom, an iodine atom, or a bromine atom; Z represents an aryl group; R1 to R19 may be the same or different and each represents a hydrogen atom, a fluorine atom, an alkyl group, or a fluoroalkyl group; and a and b each represents an integer of 1 to 20.
The halogenated aromatic compound provides a (co)polymer with a structure that is readily sulfonated to enhance the effective sulfonation of the (co)polymer.
Second, the invention is to provide a polyarylene (co)polymer having a repeating unit represented by the following general formula (1b): 
wherein A, B, Z, R1 to R19, and a and b are the same as defined above.
The polyarylene (co)polymer may be a homopolymer or a copolymer containing other repeating units.
Third, the invention is to provide a polyarylene copolymer having a repeating unit represented by the general formula (1b) and a repeating unit comprising other divalent aromatic group.
Fourth, the invention is to provide as one of the foregoing copolymers a polyarylene copolymer wherein the repeating unit comprising other divalent aromatic group is a unit presented by the following general formula (1a): 
wherein Asxe2x80x2 independently represent an electron-withdrawing group; Bsxe2x80x2 independently represent an electron-donating atom or divalent group; R20 to R27 may be the same or different and each represents a hydrogen atom, a fluorine atom, an alkyl group, or a fluoroalkyl group; and n represents 0 or an integer of 1 to 20.
Since the copolymer has a flexible structure, its toughness is enhanced.
Fifth, the invention is to provide the foregoing (co)polymer further containing a sulfonic acid group.
The sulfonic acid group-containing (co)polymer is useful as a material of proton-conductive membrane.
Sixth, the invention is to provide a proton-conductive membrane comprising the foregoing sulfonic acid group-containing (co)polymer.